1. Field of the Invention
The present invention relates to a sheet processing apparatus and an image forming system, and more particularly, to a sheet folding process.
2. Description of the Related Art
In recent years, information has been converted in a digital form, and an image processing apparatus such as a printer or a facsimile used to output digital information or a scanner used to convert a document in a digital form has become an indispensable device. Such an image processing apparatus has, for example, an image capturing function, an image forming function, and a communication function and is usually configured as a multifunction peripheral that can be used as a printer, a facsimile, a scanner, and a copy machine.
Among such multifunction peripherals, a multifunction peripheral equipped with a folding processing apparatus that performs a folding process of folding a sheet on which an image is formed after rendering an image by forming an image on a fed sheet has been known. Typically, the folding processing apparatus includes a folding processing roller pair configured with two folding processing rollers laterally bridging in a direction parallel to a folding line to be formed, and forms a folding line at a folding position by pinching a bend formed at the folding position from both sheet surfaces through the folding processing roller pair while rotating the folding processing roller pair (for example, JP 2012-144312 A).
At this time, the folding processing apparatus generates pressing force over the whole area in a direction perpendicular to a sheet conveyance direction by applying force for pressing the folding processing rollers against each other in both ends of the folding processing roller pair in the direction perpendicular to the sheet conveyance direction. Thus, in the folding processing apparatus, when the sheet is pinched by the folding processing roller pair, repulsive force is generated from the sheet against the pressing force, but the force of pressing the folding processing roller against each other acts as a force countering the repulsive force near both ends in the direction perpendicular to the sheet conveyance direction, and thus the sheet can be sufficiently pressed by the force although the repulsive force acts.
Meanwhile, in the folding processing apparatus according to the related art, since no force countering the repulsive force acts near a central portion in the direction perpendicular to the sheet conveyance direction, when the repulsive force acts, the folding processing rollers are bent in a direction opposite to a pressing direction, and thus there is a problem in that it is difficult to sufficiently press the sheet.
Further, in the folding processing apparatus according to the related art, since the force for pressing the folding processing rollers against each other acts on both ends of the folding processing roller pair in the direction perpendicular to the sheet conveyance direction, a deviation of pressing force occurs between both ends. As a result, in the folding processing apparatus according to the related art, it is difficult to press the sheet evenly at one end and the other end, and a wrinkle or a skew occurs in the sheet, or the folding position is misaligned, resulting in a reduction in a folding quality.
Therefore, there is a need for a sheet processing apparatus and an image forming system capable of forming a folding line on a sheet effectively and improve a folding quality.